Abstract Increasing enrollment and greater reliance on after-school programs (ASPs) for social emotional learning (SEL) coincides with research demonstrating that participation in high quality ASPs contribute meaningfully to positive youth development and mental health, especially for youth living in communities of concentrated urban poverty. These benefits rely on high quality experiences in a supportive environment with structured youth- adult interactions and well-organized opportunities for engagement. However, organizational and workforce variability across ASPs underscores the myriad challenges associated with consistent, high quality, and sustained SEL programming in ASPs. The traditional model for professional development (PD) and implementation of SEL curriculum in schools does not transfer to the after-school setting. Hence, we propose a technology-based innovation for ASP provider training in SEL programming that harnesses strengths, acknowledges limitations, and leverages opportunities inherent to diverse and complex ASPs. To our knowledge, the proposed product will be the first technology product that provides self-paced interactive instruction and practice to build workforce skills necessary for after-school providers to create and capitalize on teachable moments during after-school routines and recreation to meet the social, emotional, and behavioral needs of enrolled youth. This 12-month SBIR Phase I project will accomplish three specific aims: (1) develop a fully functioning software prototype; (2) conduct prototype usability and feasibility testing with frontline ASP youth care workers; and (3) conduct prototype testing with organizational stakeholders. The proposed SBIR project will directly address the need for innovative cost- and time-efficient solutions to engage after-school frontline providers in PD. The online curriculum will extend our team's public health approach to professionalizing ASP youth care workers to improve program quality and, ultimately, improve social, emotional, and behavioral outcomes for youth. Iterative development and testing will enhance and document the benefits of our proposed online PD curriculum to elevate the role of ASP youth care workers to ASP professionals. Our goal is to support broad scale dissemination and use of our online SEL training suite for ASP providers. We will market the final product as a cost and time efficient means to address the PD training needs of the more than 625,000 frontline youth care workers in the U.S. after-school market.